1. Field of the Invention
The present invention relates to a piston having a hardened primary compression ring groove and the method of making same. More particularly, the invention relates to the use of a laser in hardening the primary groove.
2. Prior Art
A piston, such as one proposed for use in a locomotive engine, takes much abuse during its function. Further, to keep forces of combustion taking place against a head of the piston, from escaping around the piston, a plurality of compression rings are seated about the circumference of the piston, each ring engaging within a groove for same provided in the circumference of the piston head.
It is known that the land defining a bottom surface of the primary ring groove is stressed significantly because the force of each combustion episode is borne primarily by the first compression ring.
To accommodate the stress placed upon the land defining the bottom surface of the primary groove, the area of the piston head incorporating the primary groove presently is hardened by induction hardening. Such induction hardening effects a large area of the piston head surrounding the ring groove, hardening parts of the piston head to no functional advantage. Rather, such large area hardening has been found to be detrimental to longevity of the piston, often leading to stress cracking of the dome or combustion head surface of the piston.
As will be described in greater detail hereinafter, laser hardening of only the functional area of the primary ring groove defined by the bottom groove surface forming land significantly increases piston head longevity.